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Using positron emission tomography (PET) and equilibrium imaging with oxygen-15 labelled gases, the cerebral blood flow (CBF), blood volume (CBV), oxygen extraction fraction (OEF) and oxygen consumption rate (CMRO₂) were measured in multiple regions of interest over the cerebral cortex of 5 control subjects, 4 patients with strictly unilateral longstanding carotid artery occlusion, 1 patient with middle cerebral artery embolic stroke in the acute stage, and 4 patients with subcortical stroke and no cervical arterial disease. In each control subject, the regional CBV was linearly and positively correlated with both CBF and CMRO², while the local mean transit time (t = CBV/CBF) was uniformly distributed, reflecting the local adaptation of both the vascular tone and the capillary density to the metabolic demand at constant cerebral perfusion pressure that characterizes the normal brain. In patients with subcortical …